1. Field of the Invention
This invention relates in general to a method of fine particle stabilization by negative charge reduction by use of cationic polymers to increase recovery of mineral and metals during chemical leaching of earth material.
2. Description of the Prior Art
It is well known that the disadvantages of the prior art of leaching in clay bearing ores was that there was no successful way to maintain colloid stability to prevent permeability loss. In situ leach mining operations often encounter difficulty maintaining adequate leach solution flow into the ore formation. Swelling and dispersion of clay particles in the formation are often responsible for this permeability loss. In situ leach mining of uranium involves injecting a carbonate-bicarbonate (basic) or sulfate (acidic leach solution (lixiviant)) through injection wells into an ore body where the lixiviant dissolves the uranium from the ore. The lixiviant bearing the complex uranium is then brought to the surface through production wells. Uranium is recovered from the lixiviant by an ion-exchange method.
Plugging of the injection wells is often a problem in in-situ leach mining. It may be caused by improper well construction, invasion by solid particles from drilling fluids or cementing operations, precipitation of chemical salts, bacterial effects, fine particles in the injection fluid, and/or clay swelling and dispersion. Acid or water jet perforation can be used to stimulate wells that exhibit high resistance to injection, but the treatments are not universally applicable and the benefits are generally temporary.
Uranium is most commonly leached from sandstone host rocks, and certain of these formations are water sensitive. Such formations are susceptible to permeability damage by exposure to introduced water that has a chemical composition different from the natural, interstitial water. The introduced water can upset the swelling equilibrium of the clay-water system.
A formation's susceptibility to permeability damage is related to the salinity of the water to which it is exposed and to the type and amount of clay mineral constituents present. Reduction in salinity of interstitial water can cause clay swelling, which may plug pores and reduce permeability. Swelling also causes the clay platelets to break up into finer, negatively charged particles. These negatively charged particles will repel one another and, therefore, disperse through the interstitial fluid until they lodge in constrictions in permeability channels, thereby plugging the channels.
The common swelling-clay minerals are the montmorillonites, mixed-layer clays, and certain types of illite. The clay particles in their natural state are at equilibrium with the saline water that usually occurs in the formations. Swelling occurs when fresh water replaces the saline water in the formation during drilling or leaching activities. In general the amount of swelling increases with a decrease in salinity of the injected water. Therefore, a concentrated brine would cause the least damage and fresh water the most damage. The nature of the clays is also important. Clays in the calcium form do not disperse as easily in low-salinity water as do clays in the sodium form. It is thought that sodium clays dissociate in low-salinity water, creating sodium ions and clay particles with a net negative charge that is great enough to cause the particles to repel one another and thus be dispersed.
The form of clay can be altered by flowing a solution through it. Through cation exchange, a sodium clay may be changed to a calcium clay by passing a concentrated calcium-bearing solution through it. The cation-exchange capacity of the clay minerals is due to broken bonds, substitution within the lattice structure, and replacement of the hydrogen of exposed hydroxyls by the exchangeable cation. It is thought that if at least one-tenth of the dissolved salts in the water are magnesium and calcium, swelling and dispersion of clays will be minimal. The hydrated calcium and magnesium ions seemingly restrict the adsorbed water on the clay to a well-developed configuration of minimal thickness, whereas the sodium ion allows oriented water to grow to very great thicknesses on the clay.
For that reason in situ uranium leach mining operators often use native ground water to prepare the leach solution because it usually contains calcium and magnesium ions. The leach solution, however, may still cause changes in formation water chemistry great enough to cause the clay to swell, and if the clay is in the swelling or dispersing form, any fluid flowing through the formation will result in permeability damage.
Commercial clay stabilizers have been developed to reduce permeability loss due to clay swelling and dispersion. Inorganic clay stabilizers include hydroxyl aluminum and zirconium oxychloride solutions. The higher charge cations of these clay stabilizers will adsorb on the clays more readily than monovalent or divalent cations because the attractive force between the negatively charged clay particles and the stabilizer cations is exponentially related to the charge on these cations. These clay stabilizers have been shown to be effective in reducing permeability losses, but removal of these cations from the clays may occur when and if the wells undergo acid treatment. A series of acid-resistant, organic polymer clay stabilizers have also been developed to prevent permeability losses in water-sensitive formations under a broad range of operating conditions.
These and other problems are well known and a wide variety of methods have been used. For example, U.S. Pat. No. 4,008,134 to Thomsen is based on a combination of leaching the metal-containing raw materials with an organic acid (cation exchange) and a subsequent use of the formed metal cationic complex in a liquid-liquid extraction process. U.S. Pat. No. 4,360,500 to Fly, relates to hydrometallurgy for supplying, separating and assorting solids in liquid suspension by a vertical current.
Also at the time of filing this application, applicant was familiar with the following U.S. patents:
U.S. Pat. No. 4,017,309 to Johnson PA1 U.S. Pat. No. 4,080,419 to Engelman PA1 U.S. Pat. No. 4,342,222 to Alekhim et al PA1 U.S. Pat. No. 4,385,666 to Momadzahanov et al PA1 U.S. Pat. No. 4,410,052 to Momadzahanov et al PA1 U.S. Pat. No. 4,473,115 to Oakes PA1 U.S. Pat. No. 4,606,765 to Ferlay